400 Ex Jetting!!

[Pont400ex]

I have a 2001 Honda 400ex with a 408 kit, High compression piston, Stage 1 hot cam, full yoshi exhuast, aluminum airbox with no cover, with a k&n filter. My problem is my headers glow after i ride for a bit, i dunno the jetting now, but it isnt jetted for the aftermarket parts, I know its not a bent valve because i just had those cleaned and inspected. If someone could tell me what size Main and what size pilot to use for jetting i would greatly appreciate it. Thanks it advance

go to www.jetsrus.com tand read the faq to the left on jets and jetting to get a better understanding of jetting...

[Pont400ex]

Thanks for the reading. It helped a little but i still dont know what size jet to use.

[dbc112]

400ex stock pilot is 38 and main is 148. It sounds like you are running lean, check the jetsrus article on spark plugs and check the color of yours...


If you are lean, go to the local shop and get a couple of sizes of keihin main jets, try 155, 158.. 152 may be to conservitve... but hard to tell. Also your mixture screw should be 2 1/4 turns.. To do this, turn it in until you get some resistance from the rubber thingy.. Then turn 2 /14 out.


I have a 300ex with full built national kit running a 400ex carb. I recently left the idol jet at 38 and changed the main to a 155.


it seems to work for me now...


Another thing you can try is running with the choke half way up. Deprive the engine from some air and make it run a little more rich. See if you get the glow. Dont do this all the time because it is bad for the motor apparently (not sure why honda service tech told me not to)...

Jeting is so freaking easy, while you are in there spray some carb cleaner in the open holes.

I have never done it before and it literally took me 30 min to take apart and clean. Of course I stayed away from anything that looked hard to place back together. Just use a towel, take things out and place in the order they came out.

[Pont400ex]

I changed the pilot to 40 and the main to 160 and adjusted everything and it works well now, thanks for the info